hosts(5) -- Linux man page

NAME

/etc/hosts.equiv - list of hosts and users that are granted "trusted"
r command access to your system

DESCRIPTION

The hosts.equiv file allows or denies hosts and users to use
the r-commands (e.g. rlogin, rsh or rcp) without
supplying a password.

The file uses the following format:

[ + | - ][hostname][username]

The hostname is the name of a host which is logically equivalent
to the local host. Users logged into that host are allowed to access
like-named user accounts on the local host without supplying a password.
The hostname may be (optionally) preceded by a plus (+) sign.
If the plus sign is used alone it allows any host to access your system.
You can expicitly deny access to a host by preceding the hostname
by a minus (-) sign. Users from that host must always supply a password.
For security reasons you should always use the FQDN of the hostname and
not the short hostname.

The username entry grants a specific user access to all user
accounts (except root) without supplying a password. That means the
user is NOT restricted to like-named accounts. The username may
be (optionally) preceded by a plus (+) sign. You can also explicitly
deny access to a specific user by preceding the username with
a minus (-) sign. This says that the user is not trusted no matter
what other entries for that host exist.

Netgroups can be specified by preceding the netgroup by an @ sign.

Be extremely careful when using the plus (+) sign. A simple typographical
error could result in a standalone plus sign. A standalone plus sign is
a wildcard character that means "any host"!

FILES

/etc/hosts.equiv

NOTES

Some systems will only honor the contents of this file when it has owner
root and no write permission for anybody else. Some exceptionally
paranoid systems even require that there be no other hard links to the file.

Modern systems use the Pluggable Authentication Modules library (PAM).
With PAM a standalone plus sign is only considered a wildcard
character which means "any host" when the word
promiscuous
is added to the auth component line in your PAM file for
the particular service
(e.g. rlogin).